The invention relates generally to a safety belt retractor, and more particularly to a safety belt retractor having a brake mechanism which acts directly on the belt and operates in conjunction with a reel-locking mechanism.
A typical safety belt retractor includes a spring-biased reel on which a length of safety belt webbing is wound, and an inertial reel-locking mechanism which locks the reel against rotation to prevent protraction of the webbing in the event of a situation where passenger restraint is needed. Locking of the reel does not necessarily preclude any further protraction of the belt, because the webbing may cinch on the reel when under high tension. Several proposals for improved retractors provide for a mechanism which clamps or grips the webbing directly to stop protraction, either in conjunction with or instead of the reel locking mechanism. While such clamping arrangements may provide improved control over belt protraction, they also present certain problems.
One problem is that the gripping or clamping mechanism must engage the webbing securely enough to arrest its movement while the webbing is subjected to a high tensile load, without damaging the webbing. The tensile load on the belt may greatly exceed the weight of the passenger in the event of a collision. To meet manufacturing standards, the clamping mechanism must be capable of repeatedly constraining the belt against tensile loads of about 1600 lbs. without damage to the belt. A mechanism which causes fraying or other damage to the belt webbing is unacceptable even if it is otherwise effective.
A relatively early proposal for a clamping device is set forth in U.S. Pat. No. 3,467,337. As disclosed at column 4, line 15 et seq., and shown in FIG. 2, the clamp 60 in this patent has a curved edge 78 which engages the belt 29. This clamping mechanism illustrates one general approach to the problem of avoiding belt wear, in which the belt is engaged by a rough or toothed surface on one side, and a smooth surface on its opposite side, with the rough or toothed surface moving in the same direction as the belt during clamping, so as to reduce or eliminate movement of the rough or toothed surface relative to the belt. One disadvantage of the arrangement shown in U.S. Pat. No. 3,467,337 is that only a relatively small portion of the clamp surface area engages the belt due to its curvature. This may result in unacceptable stress concentrations on both the belt and the clamp.
Another proposed retractor with a belt-clamping mechanism is disclosed in U.S. Pat. No. 4,544,112, in which wedge-shaped members cooperate to clamp the belt. A problem with this arrangement is that the clamping mechanism jams, or reaches mechanical equilibrium, after closing on the belt, and cannot be opened merely by the force of the spring which provides rotational biasing on the reel. Accordingly, a manually operable release must be provided, which is inconvenient to the wearer.
U.S. Pat. No. 4,394,034 discloses a retractor in which a movable frame 40 supports a reel 70. When the reel locks, the frame travels upward and a clamping member 84 carried on the frame clamps or wedges the belt against abutment surfaces of a belt passage 100. This retractor relies on a wedging action to provide a mechanical advantage so as to enable high enough clamping forces to be achieved. However, it is believed that if this clamping mechanism is configured so as to provide sufficiently high clamping forces, it will be difficult to withdraw the clamping member from engagement with the belt after clamping occurs, without a manual release.
Another proposal is illustrated in U.S. Pat. No. 4,687,253, which illustrates various proposals for a clamping mechanism used in conjunction with a reel supported in elongated slots.
While various other proposals for clamping mechanisms have been made, such mechanisms often require a unique or complex retractor and complex wedges or wedging actuators which do not readily release the belt. The use of a conventional retractor operating in conjunction with a small and simple, pivoted belt-clamping or braking means operable by a cam which does not damage the belt and readily releases by itself has not heretofore been attained.
It is a general object of the invention to provide an improved safety belt retractor which includes a reliable brake mechanism that acts directly on the belt and operates in conjunction with a reel-locking mechanism.
Further objects of the invention are disclosed below.